Laux Plant Stem Cells

• linage mechanism (as in animal stem cell niches) [root meristem]

• population mechanism [shoot meristem]

—> in a replacement assay meaning a cell in the niche is replaced in linage it just stays in the replaced state, in population over time all cells equalize to one of the sorts

• Photoreceptor proteins, such as phytochromes and cryptochromes, perceive light signals and transmit this information to the shoot meristem.

• Gravity sensing (particularly in root cap cells) influences the orientation of the shoot, and information about gravity is transmitted to the shoot meristem to guide growth

• chemical signals, including hormones such as auxins, cytokinins, and gibberellins. These hormones act as signaling molecules that convey information about environmental conditions and influence shoot meristem activity

• changes in stomata conditions

• environmental, mechenical stress, temperature, pathogens, hormones

• it plays a crucial role in sensing and responding to environmental cues and transmitting signals to the underlying meristematic tissues

• environmental sensing, light and gravity perception

• chemical signaling and communication

• Protection and barrier function

• Photoreceptor, stress / temperature sensors

• direct contact to environmental factors and production of signaling factors

• polarized transport (from outer to inner)

1. Cell-to-Cell Signaling:

   • Hormones, peptides, and auxin gradients.

2. Mechanical Signals:

   • Cell walls, mechanical forces, and polarity.

3. Polar Transport:

   • Directional movement of molecules, especially auxin.

4. Cell Fate Determinants:

   • Asymmetric cell division and unequal inheritance.

5. Tropic Responses:

   • Gravitropism and phototropism.

6. Cell Identity and Lineage:

   • Lineage-dependent cell fates.

7. Environmental Cues:

   • Nutrients, temperature, and humidity.

8. Apical Meristem:

   • Actively dividing cells, organ primordia, and tissue organization.

1. WUS (WUSCHEL):

   • WUS (WUSCHEL) is primarily associated with the shoot apical meristem (SAM) in the aerial parts of the plant. It is involved in maintaining the undifferentiated state of stem cells in the central zone of the shoot apical meristem. WUS plays a crucial role in shoot development, organ initiation, and the transition from vegetative to reproductive growth.

2. WOX Genes in the Root:

   • Several members of the WOX gene family are associated with root development. One notable example is the WOX5 gene. WOX5 is expressed in the root apical meristem (RAM) and is crucial for maintaining the stem cell population in the root meristem. It is involved in root development, including the specification of root stem cells and the initiation of lateral root primordia.

3. WOX Genes in General:

   • The WOX gene family comprises multiple members with diverse functions in plant development. Different WOX genes are expressed in various tissues and developmental stages, contributing to the formation of specific organs and structures. WOX genes often contain a conserved homeodomain, a DNA-binding domain that plays a role in their regulatory functions.

4. Role in Meristem Maintenance:

   • Similar to WUS in the shoot meristem, WOX genes in the root meristem contribute to the maintenance of stem cells. They regulate cell division, differentiation, and organ initiation in the root, ensuring proper root growth and development.

SAM = shoot apical meristem

The interaction between WUSCHEL in the organizing center and CLV3 in the surrounding cells is crucial for the proper regulation of the shoot apical meristem, ensuring the maintenance of stem cells while preventing excessive cell proliferation. This feedback loop helps maintain the dynamic equilibrium required for normal plant growth and development

• popcorn bucket —> everything pushed outside this reach differentiate

• 3 cell sheets till WUS in organizing centre —> miR394 provides stem cell competence to the three outer cell layers

• high cytokinin/auxin balance (WOX repressing Auxin and by that differentiation) (Cytokin pathway with LOG enzyme produced in the 3 cell linages before organizing centre)

• that miR394 is not the sole determinant of epidermal fate

• additional factors needed

• miR394 provides stem cell competence to the three outer cell layers

• LCR is target of miR394 (inhibiting LCR enables stem cells)

• linage mechanism (as in animal stem cell niches) [root meristem]

• population mechanism [shoot meristem]

—> in a replacement assay meaning a cell in the niche is replaced in linage it just stays in the replaced state, in population over time all cells equalize to one of the sorts

• it can be tested by transplantations

• transplantation tests show the the whole linage of daughter cells tell the new daugther cells what they should become

• Target of microRNAs can be found by checking phenotype when miR394 and the target is present, then with miR394 absent and then with miR394 and the target absent. If the phenotypes of the 1st and 3rd are the same but the 2cd showed difference miR394 is needed to target that component

• use MIM394 (mimicing miR394) which prevents real inhibition activity and see how the different targets react if miR394 was needed they will show different response then without MIM394

• miR394 function is not required in the L1 for stem cell maintenance —> the cells that produce miR394 dont need it themselves

  
  

miRNA movement in plants is often facilitated by cell-to-cell transport mechanisms. Some miRNAs move through plasmodesmata, microscopic channels connecting plant cells

plasmodesmata closes after 3rd layer

transportproteins no longer aid or hinder further transport

the miR394 is only stable so far or is degraded after

other factors

1. Immunolocalization:

   • Antibodies, immunohistochemistry, immunofluorescence.

2. Reporter Gene Expression:

   • β-glucuronidase, green fluorescent protein, hormone-responsive promoters.

3. In Situ Hybridization:

   • RNA probes, mRNA localization, hormone synthesis sites.

4. Transgenic Plants:

   • Overexpression, knockout, altered hormone levels

5. Hormone Biosensor Proteins:

   • Fluorescent biosensors, real-time monitoring, hormone dynamics.

6. Grafting Experiments:

   • Tissue connection, systemic effects, local effects.

7. Mass Spectrometry:

   • Quantification, hormone levels, different tissues.

8. Microdissection:

   • Laser capture microdissection, specific cells, targeted analysis.

9. Pharmacological Treatments:

   • Inhibitors, biosynthetic precursors, tissue-specific application.

10. High-Resolution Imaging:

    • Confocal microscopy, live-cell imaging, cellular-level observation.

1. Benefits of Sensitivity:

   • Rapid Response: Increased sensitivity allows plant stem cells to respond quickly to stress signals, triggering adaptive mechanisms and protective responses.

   • Survival Strategies: Sensitivity can facilitate the activation of stress-related genes and pathways, leading to the production of protective compounds and the initiation of stress tolerance mechanisms.

2. Drawbacks of Sensitivity:

   • Cell Damage: High sensitivity may lead to excessive stress responses, causing cellular damage or even cell death if the stress is severe. This can have negative consequences for overall plant health and growth.

   • Energy Costs: Continuous activation of stress responses can be energetically costly for the plant, diverting resources away from growth and development.

3. Benefits of Insensitivity:

   • Conserved Energy: Lower sensitivity may conserve energy, allowing the plant to prioritize growth and development under normal conditions.

   • Reduced Cellular Damage: Insensitivity may prevent unnecessary activation of stress responses, reducing the risk of cellular damage in the absence of severe stress.

4. Drawbacks of Insensitivity:

   • Inability to Respond: Reduced sensitivity may result in delayed or inadequate responses to stress, potentially compromising the plant's ability to survive and adapt.

   • Failure to Activate Protective Mechanisms: Insensitivity may prevent the activation of stress tolerance mechanisms, making the plant more vulnerable to adverse conditions.

Ultimately, the optimal level of sensitivity for plant stem cells depends on the ecological niche of the plant and the specific challenges it faces in its environment. Evolutionary pressures shape the stress response mechanisms of plants, leading to species-specific adaptations. In agricultural contexts, researchers may explore genetic modifications to enhance stress tolerance in crops. However, it's crucial to consider the balance between stress sensitivity and the potential costs associated with prolonged stress responses.

• convergent evolution

• similarities may arise from the shared need to regulate stem cell behavior within tissues for sustained growth and development —> functional necessity, same environment